Why did the heat-killed bacteria didn't cause the death to the mice?

by Reham
(Saudi Arabia, Jeddah)

In Griffith Experiment he injected the mice with a mixture of the heat-killed disease-causing bacteria with the live & harmless bacteria the mice have died but when he injected them with only the heat-killed disease-causing bacteria ALONE the mice have lived. Why?

Can you explain what is actually happening during transformation?

I have red that the heat couldn't destroy the DNA of the disease-casuing bacteria and instead it transformed it to the harmless bacteria and changed it into a disease-causing bacteria, which leads to the death of the mice. So if that was true and the heat couldn't really affect the disease-causing bacteria why would then when Griffith injected the mice with the heat-killed disease-causing bacteria ALONE the mice have survived ? So where did the bacteria's DNA go?